Conventionally, pre-crash safety (PCS) systems are known; these PCS systems mitigate and/or avoid collision damage between an own vehicle and objects, i.e. obstacles, such as other vehicles, pedestrians, or road structures located in the travelling direction of the own vehicle. Such a PCS system obtains a time to collision (TTC) with an object based on a relative distance of the obstacle with respect to the own vehicle and a relative speed or a relative acceleration of the obstacle relative to the own vehicle. The TTC represents a margin time until which the own vehicle would collide with the obstacle. Then, the PCS system causes a warning device to provide, to the driver of the own vehicle, a warning about the approach of the obstacle, and/or activates a braking device of the own vehicle.
The PCS system has a predetermined determination zone ahead of the travelling direction of the own vehicle in order to determine whether there is a high possibility of an obstacle colliding with the own vehicle. This aims to detect any pedestrian, who has a fast lateral moving speed, approaching the own vehicle, as early as possible.
Patent document 1 describes a collision risk determination apparatus as a known technology according to such a PCS system. The collision risk determination apparatus disclosed in patent document 1 includes a vehicle-width zone, i.e. a first determination zone, established based on a predicted travelling path of an own vehicle, and pedestrian enterable zones, i.e. second determination zones, established at both lateral sides of the vehicle width zone based on the maximum moving speed of a pedestrian. The first determination zone and the second determination zones constitute a risk determination zone.
Then, the collision risk determination apparatus determines that a collision risk is high when there is a pedestrian in the risk determination zone, thus activating the PCS system.